A wireless communication system generally comprises several radio devices or posts exchanging data of any type. In the communications sector, HF linkups offer notably a beyond line of sight or BLOS capability which makes it possible to achieve communications at long, or indeed very long distance, without requiring recourse to a satellite or to the use of relay stations. Nonetheless, the quality of the communications varies as a function of atmospheric conditions, the ionospheric medium being extremely variable. In the VHF or UHF band the propagation channel fluctuates less but mobile deployments can lead to cases of jamming on account of a desire for spatial reuse of the frequencies, thus also giving rise to fluctuations in the quality of the channel, depending on the frequencies used.
One of the subjects of the invention relates to link setup between two radio posts. Of more particular concern hereinafter is the case of HF posts, wherein at least one calling post has a broadband operating capability (transmission and/or reception) and wishes to determine a communication band usable for a bandwidth of greater than 3 kHz. This value corresponds to what is offered by the current standards, whether involving the linkup establishment solution automatically, termed second-generation and known by the abbreviation 2G ALE (2G automatic link establishement) according to the MIL STD 188-141A standard, with or without proprietary variants, or termed third-generation or 3G ALE according to the STANAG 4538 standard, with or without proprietary variants. This type of link setup is particularly of interest in respect of posts capable of employing an aggregate of several HF channels such as, for example, proposed in annex D of the MIL STD 188-110C standard, wherein is described the use of several contiguous carriers of 3 kHz or of the generalized use such as described in the patent applications FR 10.04560 and FR 11.03083 of the Applicant or of standards which use a single-carrier waveform, according for example to annex D of the MIL STD 110-188C standard.
The state of the art known to the Applicant proposes various techniques for HF broadband link setup and link sustaining.
A first technique consists in performing a 3 kHz conventional link setup and in arbitrarily widening the use around, optionally with a shift (offset), the central frequency with respect to the initial frequency, even if this results in decreasing the band used or in relaunching the procedure if the band is used. This technique exhibits the risk of jamming of already used frequencies. There is indeed no assurance that there are bands available around this frequency selected by the ALE, and the duration of convergence is unknown.
A second technique relies on a 3 kHz conventional link setup and listening to the band around, so as to determine whether sufficient available band for transmitting in broadband is found. There is however no assurance that there are available bands around this frequency selected by the ALE, and the duration of convergence is once again unknown, this possibly leading to a potentially lengthy solution.
A third solution consists in carrying out as many 3 kHz link setup procedures as bands considered and deciding as a function of the measurements made on the possible communication linkups. This solution leads to a necessarily slow mechanism, whose convergence may even be problematic if initially free frequencies are occupied meanwhile in the course of the procedure.
A fourth solution described in patent application EP 2 418 892 entitled “High frequency automatic link establishment communication system with wideband probe and related method”, carries out an innately broadband link setup from 6 to 24 kHz on the basis of a robust single-carrier frequency F0 to evaluate the occupancy of a 6 to 24 kHz channel and to retain the widest possible free span in this channel. This technique applies only in respect of contiguous bands.
Despite all the advantages offered by the various techniques known from the prior art, the existing solutions based on 3 kHz link setup do not make it possible to evaluate the quality of the adjacent channels dynamically, unless a very large link setup time is accepted. The solution based on a 24 kHz carrier such as described in patent application EP 2 418 892 does not make it possible to evaluate a plurality of channels distributed over more than 24 kHz, or to readily adapt the waveform in the case where the initial frequency is surrounded by disturbed channels.